In the related art, there has been a technology called MWD (Measurement While Drilling) for measuring information regarding the inside of a drilled hole in real time, as an important technology in resource drilling for petroleum or the like and scientific drilling MWD uses a transmission technology that generates back pressure (pressure against the direction opposite to a circulation flow) called mud pulses (drilling mud pressure waves) and uses the phase difference and the frequency difference between the pressure waveforms (for example, see Patent Literature 1)